Internal combustion engines use only a portion (for example, approximately 31% to 38% in some cases) of the supplied fuel energy due to heat wasted, friction, incomplete combustion, and others. In addition, approximately 3-17% of the supplied fuel energy can be used to maintain the engine operation during standby and another 1-2% can be used to operate accessories. Therefore, it can be advantageous to utilize the waste energy, typically in the form of thermal and chemical energy, to improve the overall vehicle system fuel efficiency.
One approach uses a solid oxide fuel cell (SOFC) arranged in an exhaust system of an internal combustion engine, such as described in U.S. 2004/0177607. In the '607 reference, a power generation fuel can be supplied to the fuel cell by a fuel supply system downstream of the engine and upstream of the fuel cell so that electricity can be generated without depending on the operation condition of the engine. Some embodiments of the 607′ reference include an oxidation catalyst upstream and downstream of the SOFC. The upstream oxidation catalyst is used to oxidize unburnt fuel from the engine, thus raising temperature of the exhaust gas discharged from the engine. Another role of the upstream catalyst is to reform unburnt fuel. The downstream oxidation catalyst is used to oxidize fuel discharged from the SOFC without undergoing reactions.
However, the inventors herein have recognized several disadvantages of such an approach. For example, the NOx emissions may not meet the related regulations since neither the upstream nor the downstream oxidation catalyst is aimed at reducing the NOx emissions. Further, some fuel reformed in the engine such as hydrocarbon and carbon monoxide may be oxidized in the oxidation catalyst, and thus cannot be used as effectively for power generation fuel for the SOFC.
Furthermore, the inventors herein have recognized that since '607 approach operates engine independent of the fuel cell, there are conditions that energy from engine may be wasted to a great extent and emissions from the system may not meet the standards.